Not Applicable
1. Field of the Invention
The present invention relates to a method for reconditioning, retrofitting or upgrading existing, previously used, propane gas cylinders from a standard unprotected plain cylinder to a substantially explosion resistant cylinder that is safer in all threat situations. Generally, the present invention relates to fuel tanks used for flammable or explosive fluids such as gasoline, diesel fuel, butane and LP-Gas; and, more particularly, to upgrading used tanks or cylinders by (a) employing rolled aluminum inserts with clips to fill substantially the cylindrical interior with minimal flaking of the aluminum inserts and providing with such inserts additional internal wetted surface areas within the tank to increase the efficiency discharge rate of explosive fluids"" vapors in the tank, (b) changing a relief valve for the tank to a higher CFM (cubic feet per minute) discharge rate thereby to eliminate heated vapors faster, (c) applying a coating to the cylinder of calcium carbonate/calcium sulfonate complex and (d) adding an outer sheet, sheath, sleeve or wrapper of composite fiber fire resistant material having projections or bumps on its outer periphery around the tank and in this way address the problem that occurs with aluminum tanks which tend to lose structural integrity when exposed to high heat.
2. Description of the Prior Art
There are millions of used LP-Gas cylinders, both steel and aluminum, is that are in use today in the United States. They do not have any type of internal protection from explosions other than a relief valve to relieve vapor over-pressures when they are exposed to fires, punctures, ballistics and other such threats. These aluminum cylinders are getting old and can possibly be a major explosion hazard within the next few years. However, if they can be upgraded and re-certified without any major changes, then the metal of the tank or cylinder may be able to withstand over-pressures caused by faulty relief valves. Many people are injured or killed because of malfunctioning clogged, stuck and/or faulty relief valves. In a typical LP-Gas application there is generally provided a metallic tank wall designed to contain the fuel under pressure. This tank is typically of steel or aluminum composition for portable applications (motor fuel, portable LP-Gas applications) and further includes associated valves and connections at one end for gaining access to the contents of the tank or cylinder. There is also a pressure relief valve at the same end as the access connection. When the tank is in a heated environment, such as a fire, the fluid or liquid proximate a hot spot on the wall of the tank will boil and eventually ignite, with a resulting explosion. Prior attempts to neutralize the explosion tendencies of the tank have included providing at the initial point of manufacture of the tank, an expanded aluminum foil mesh as a filler mass insert. Such a system is described in Canadian Patent No. 736,802. The container is filled with the mesh, which divides the container into many small cell-like compartments, and through the mesh the fuel transfers the heat away from the xe2x80x9chot spotxe2x80x9d to delay the local rise in temperature and a deadly explosion.
Improvements in tank design have recently been directed to preventing nesting of the mesh insert by reversing alternate layers in a roll. This is done when the tank is newly manufactured. Nesting occurs where the mesh pattern of adjacent layers settle against each other in a mating relationship.
A recent anti-nesting system is described in U.S. Pat. No. 4,149,649. Even with the anti-nesting pattern of the prior art, the lightweight foil in the mesh tends to collapse and compress and its effectiveness diminished during use; this is particularly true for transportable containers, motor fuel containers and vehicular fuel tanks.
Recently a new technique was developed for heat transfer from aluminum mesh inserts to the wall of a fuel tank, which is described in U.S. Pat. No. 4,673,098 issued to Fenton et al., and which dramatically improved the thermal conductivity to the tank wall and which reduced the compression effect.
In the vehicle and lift truck tank industry, where weight is of a high importance, tanks of aluminum composition are extremely popular and have been in service for over 20 years.
Unfortunately, the aluminum tank wall tends to melt at a lower temperature than steel tanks such that its structural integrity is quickly lost in a fire. Adding to this is the fact that existing relief valves are often clogged and dirty and will not always open as designed which causes the wall to fail sooner than its designed fail point, causing catastrophic explosions.
Attempts to insulate or coat the outer surface of such tanks have proved unsatisfactory inasmuch as the coating does not remain sufficiently intact to produce consistent reliable results.
It is a feature of the present invention to provide an explosion reduction method for used aluminum cylinders that will be functional with transportable containers including lift truck cylinders and vehicle tanks.
According to the method of the present invention, the old relief valve is first removed and small clipped aluminum foil inserts are pushed into the cylinder until they are fully packed to the top of the valve opening. The inserts provide the additional wetted surface area required to initiate additional efficient vaporization within the tank. The aluminum filler mass inserts are impervious to propane and take up less than 3% of the liquid volume of the tank. Aluminum foil filler masses in large sheet form have been used in propane cylinders since 1991 without a single incident of injury or death, although they were exposed to fires and other types of threats.
It is a further feature of the method of the invention, when the cylinder is being upgraded, to provide a new relief valve rated at a higher CFM dischargerate than is presently being installed on new aluminum cylinders. This new higher CFM rated valve will allow a greater rate of discharge from the pressurized overheated tank.
Propane vapor is more readily created by the added aluminum foil filler mass inserts. These filler mass inserts provide additional wetted surface area within the tank and create more efficient vaporization rates when heat is being applied to the container. This will reduce the chance of the tank wall failing in the used container that has been subjected to heat and will allow more time for persons to evacuate the immediate area.
Another feature of the method of the present invention is to install a fiber/resin composite outer wrapper on the tank that slips over the outer wall of the tank. This will provide a fire resistant shield to reduce any heat applied to the outer wall and will further strengthen the outer wall of the cylinder. This wrapper is molded to fit the outer wall of the container and it will snap into place when it is installed over the top of the cylinder. The wrapper has raised ribs and/or bumps to help keep the wall of the cylinder free from dents and scratches. If desired, the wrapper may be glued to the outer wall of the cylinder with a fire resistant adhesive (e.g., 3M EC776).
Finally, the added wetted surface of the internal filler mass established by the aluminum inserts provides additional pressure for opening the relief valve when the cylinder is exposed to heat. This will help unclog and open the relief valve which has been subjected to dirt and other contaminants that would otherwise cause the relief valve to become stuck and malfunction. Since a clogged relief valve will not normally open fully, the added pressure from the added wetted surface within the tank will help to unclog the relief valve, thus relieving the over-pressure within the tank and thereby avoiding an explosion.
It is a further feature of the invention to use existing used aluminum cylinders that have been in service, with a low cost to upgrade or convert them to a safer cylinder that will have less tendency to rupture and cause injury or death to those persons exposed to that type of hazard that these used cylinders present.